1. Technical Field
The present invention relates to deep trenches, and more particularly, to the formation of a deep trench in a semiconductor substrate.
2. Related Art
Deep and narrow trenches have been used for several purposes in semiconductor devices, one of which is to serve as storage-capacitor structures. Typically, a deep trench is created in a semiconductor substrate by first forming a hard mask layer (which itself can comprise multiple layers) on top of the semiconductor substrate. Then, an opening is created in the hard mask layer. Next, through the opening, etching of the deep trench in the semiconductor substrate is performed. During the etching of the deep trench, energetic, heavy ions are used to bombard the bottom of the deep trench so that chemical etching reactions can continue downward. However, this ion bombardment can also break through the polymer layer on the side walls of the deep trench and cause damages to the side walls of the deep trench. These damages to the side walls of the deep trench may detrimentally affect the quality of the resulting device.
Therefore, there is a need for a novel method for forming a deep trench that eliminates (or at least reduces) the damage to the side walls of the deep trench which occurs during the etching of the deep trench.